Move middleware to interfaces.

This makes separating middlewares from the core api easier.
As an example, the authorization middleware is moved to
it's own package.

Initialize all static middlewares when the server is created, reducing
allocations every time a route is wrapper with the middlewares.

Signed-off-by: David Calavera <david.calavera@gmail.com>
Upstream-commit: 8d3467626ee26cad48ad84f2181552dce7afccb6
Component: engine

components/engine/api/server/server.go

@@ -8,8 +8,8 @@ import (
 
 	"github.com/Sirupsen/logrus"
 	"github.com/docker/docker/api/server/httputils"
+	"github.com/docker/docker/api/server/middleware"
 	"github.com/docker/docker/api/server/router"
-	"github.com/docker/docker/pkg/authorization"
 	"github.com/gorilla/mux"
 	"golang.org/x/net/context"
 )
@@ -20,13 +20,12 @@ const versionMatcher = "/v{version:[0-9.]+}"
 
 // Config provides the configuration for the API server
 type Config struct {
-	Logging                  bool
-	EnableCors               bool
-	CorsHeaders              string
-	AuthorizationPluginNames []string
-	Version                  string
-	SocketGroup              string
-	TLSConfig                *tls.Config
+	Logging     bool
+	EnableCors  bool
+	CorsHeaders string
+	Version     string
+	SocketGroup string
+	TLSConfig   *tls.Config
 }
 
 // Server contains instance details for the server
@@ -34,8 +33,8 @@ type Server struct {
 	cfg           *Config
 	servers       []*HTTPServer
 	routers       []router.Router
-	authZPlugins  []authorization.Plugin
 	routerSwapper *routerSwapper
+	middlewares   []middleware.Middleware
 }
 
 // New returns a new instance of the server based on the specified configuration.
@@ -46,6 +45,12 @@ func New(cfg *Config) *Server {
 	}
 }
 
+// UseMiddleware appends a new middleware to the request chain.
+// This needs to be called before the API routes are configured.
+func (s *Server) UseMiddleware(m middleware.Middleware) {
+	s.middlewares = append(s.middlewares, m)
+}
+
 // Accept sets a listener the server accepts connections into.
 func (s *Server) Accept(addr string, listeners ...net.Listener) {
 	for _, listener := range listeners {